1. Field of the Invention
The present invention relates to a system and method for driving a hybrid electric vehicle, and more particularly, to a driving system and driving method of a hybrid electric vehicle, wherein driving of a hybrid electric vehicle is controlled according to a determined traveling mode.
2. Description of the Related Art
A Hybrid Electric Vehicle (HEV) refers to a vehicle using driving force outputs of both an internal combustion engine and an electric motor. As compared to a typical vehicle equipped with only an internal combustion engine, such a hybrid electric vehicle is able to remarkably reduce the amount of exhaust gas and thus, is usually referred to as an “eco car”.
FIG. 1 is a view illustrating the configuration of a power train of a conventional hard-type hybrid electric vehicle.
Referring to FIG. 1, the power train of the conventional hybrid electric vehicle includes an internal combustion engine 1, an engine clutch 2 connected to an output end of the internal combustion engine 1, a carrier gear 3 connected to the engine clutch 2, a sun gear 6 connected to a generator 7, a ring gear 4 connected to an electric motor 5, and pinion gears 9 connected to the ring gear 4, sun gear 6 and carrier gear 3. Here, the electric motor 5 and generator 7 may take an Integrated Starter & Generator (ISG) configuration capable of simultaneously achieving power generation and transmission. In the drawing, reference character B represents a bearing.
Generally, the conventional hybrid electric vehicle includes a Hybrid Control Unit (HCU) to control operations of the internal combustion engine 1, generator 7 and electric motor 5 according to a traveling mode of the vehicle, in order to allow the hybrid electric vehicle to be driven while maintaining an optimum state thereof. Here, traveling modes of the driving system of the conventional hybrid electric vehicle may be classified into a Hybrid Electric Vehicle (HEV) mode, an Electric Vehicle (EV) mode and a maximum (MAX) torque mode, according to a required torque, the State of Charge (SOC) of a battery, and the like. The HEV mode is a traveling mode wherein the HCU drives the hybrid electric vehicle using both the internal combustion engine 1 and the electric motor 5. In the EV mode, only the electric motor 5 is operated by power of a battery. In the MAX torque mode, the hybrid electric vehicle is driven by both the internal combustion engine 1 and the electric motor 5 in such a manner that, if a required torque is not fulfilled by the HEV mode, the internal combustion engine 1 is operated at a maximum torque, and the remaining part of the required torque is fulfilled by the electric motor 5. In addition, the hybrid electric vehicle may be driven in a regeneration mode, wherein the battery is charged while a braking force is applied to the vehicle.
FIGS. 2 to 5 are views illustrating power transmission relationship for different traveling modes of the conventional hybrid electric vehicle.
The conventional hybrid electric vehicle is able to be driven, in different traveling modes selected according to driving speeds thereof, under operation of the driving system. More specifically, upon start or low-speed traveling of the hybrid electric vehicle, as shown in FIG. 2, drive wheels W of the hybrid electric vehicle are rotated by a driving force output from the electric motor 5 as the electric motor 5 receives electric power from a battery 8. During typical traveling, as shown in FIG. 3, the hybrid electric vehicle is driven via combination of the internal combustion engine 1 and the electric motor 5 according to a driving speed thereof. In particular, upon high-speed traveling, the drive wheels W of the hybrid electric vehicle are rotated by driving force outputs from both the internal combustion engine 1 and the electric motor 5 in such a manner that power from the electric motor 5 assists power of the internal combustion engine 1. In addition, When the hybrid electric vehicle is reduced in driving speed, as shown in FIG. 4, recovery of energy is possible as the battery 8 is charged using the electric motor 5 as a generator. Upon stoppage of the hybrid electric vehicle, as shown in FIG. 5, operations of both the internal combustion engine 1 and the electric motor 5 are automatically stopped, reducing unnecessary fuel consumption and emission of exhaust gas.
Additionally, with the HCU of the conventional hybrid electric vehicle, electric power is able to be generated via the generator 7 using a braking force that is applied by both the internal combustion engine 1 and the electric motor 5 when the hybrid electric vehicle is reduced in driving speed. The battery 8 is charged with the generated electric power. For reference, energy to be used by the generator 7 for generation of electric power is referred to as regenerative energy.